So this is a pretty simple guide but worth highlighting for anyone who hasn't noticed this brilliant way of leveling your new fishing artifact yet!
First off, head out to Stormheim. The spot I like to fish is at 38:60 right next to the Lornas Watch flight point. Stick on an Arcane Lure and get fishing
Once you fish up an Ancient Vrykul Ring you can just go ahead and activate it straight away. If you're fishing in my spot a pool of Oodelfjisk should appear more or less right next to you.
You've got about 5 minutes or more (dependant on the level of your artifact) to spam fish that pool. The pools seem to be bottomless, so they last as long as you have the buff.
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On my last attempt I got 31 fish from my 7 minute buff.
Not sure if working as intended?
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Edit: Just tested and looks as though its the same story for Ghostly Queenfish. Though I find there are usually more hostile mobs near their pools.